102 SODIUM PHOSPHATE (DISODIUM PHOSPHATE)
by iron or by oxalic acid (i c.c. = 0-028 gram Fe ~ 0-0315 gram crys-
tallised oxalic acid).
10 grams of the nitrite are dissolved in water to I litre. 20 c.c. of the
permanganate solution are mixed in a conical Husk with about 130 c.c. of
water and a little dilute sulphuric acid and the liquid heated to 40-50°,
the nitrite solution being then run in from a burette1 until the colour dis-
appears, i c.c. N/2-KMn()4 = 0-01725 gram NaN()2) so that 20 c.c. =
0-3450 gram, and the percentage of nitrite is given by 3450 -••;-• ;/, where n is
the number of c.c. of nitrite solution used.
Commercial sodium nitrite generally contains 97 -<j«.)% of NaNO,,.
NaB03 + 4H..O -- 154
White powder or colourless crystals, slightly soluble in cold but readily
in hot water with liberation of oxygen ; with sulphuric acid it. gives hydro-
gen peroxide. Its value depends essent.iu.lly on the content of actual per-
borate or active oxygen, which is determined with permanganate as in
barium peroxide (</-V-}. i c.c. N/^-permanganate ; . 0-01483 gram of
NaB03 -f- 4HaO ~ 0-0016 gram of oxygen.
Commercial sodium perborate is usually guaranteed to r.ouiain 10% of active
oxygen (theoretically 10-4%).
Na,,O2 .---.: 7«
Hygroscopic white or yellowish powder, decomposed by water with
evolution of oxygen. It may contain, us impurities, sodium hydroxide
and carbonate, sulphates, chlorides, phosphates, iron and alumina, which
may be detected by the tests indicated under "Potassium Hydroxide."
Its value depends on the content of Na,,(),,, wl
sufficiently exactly for technical purposes by titr;
(sec Barium Peroxide), but the peroxide must be added to the sulphuric
acid with great care;, i c.c. N/5-permnnganatc . 0-0078 gram Na-,()».
An exact determination may be made by Arelibuit and (irossniann's
method, which consists in decomposing the peroxide with water in presence
of a little cobalt nitrate ami measuring the volume of oxygen evolved,
Lunge's nitrometer or gas-vohnnometer or similar apparatus being used.1
Commercial sodium peroxide (well stored) contains on the average 95% of
Na20B; its content in, Fe,/);, + AL/)., should not exceed 0-01%.
may be determined
SODIUM PHOSPHATE (Disodium Phosphate)
Na.,HP04 + i2llaO -358-3
Colourless, readily efflorescent, more or less large; crystals, soluble in
water to a faintly alkaline solution. The commoner impurities are car-
1 Sec Analyst, 1895, p. 3; Chem. Zeitunfo 11)05, p. ijH.llisation at 100°. The dehydrated salt, is also sold in large quan-